1. Field of the Invention
This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to a kinematic arrangement of gearing, clutches, brakes, and the interconnections among them in a power transmission.
2. Description of the Prior Art
Light trucks have been offered for sale with a variety of optional axle ratios. Customers that plan to tow heavy trailers usually order axles for such trucks that have higher torque ratios in order to get better performance when the vehicle is heavily loaded. Customers that do not plan to tow heavy trailers choose axles with less torque multiplication in order to get better highway fuel economy.
The steeper axle ratios improve vehicle launch capability when loaded, but reduce fuel economy even when the vehicle is unloaded. Providing multiple axle ratios adds complexity at the vehicle assembly plant. Operators of light truck having 4×4 drivelines seldom use the low-range capability of a two-speed transfer case.
Light trucks having 4×4 drivelines frequently offer a low-range capability within the transfer case. A very low ratio in the transmission would allow this feature to be offered in trucks with 4×2 drivelines and reduce the cost of transfer cases.
Most operators of such vehicle are accustomed to and prefer that the transmission provide a small first gear-second gear step. Eight-speed transmissions that have been proposed have gear mesh losses that exceeded those of highly efficient six-speed transmissions.
There is a need for a transmission that provides sufficient speed ratio span, such that all vehicles can have superior towing capability and also have superior highway fuel economy whenever the vehicle is not towing a heavy load. In order to accomplish this objective, the transmission should provide similar ratios to a state of the art six speed automatic transmission plus an additional low range gear.